A battery is largely classified into primary and secondary batteries, wherein the primary battery, which is a battery of producing electricity by a non-reversible reaction to be non-reusable after the battery is used once, includes a dry battery generally used, a mercury battery, a Volta's battery, and the like, by way of an example; meanwhile, the secondary battery, which is a battery of using a reversible reaction to be reusable by charging after being used, unlike the primary battery, includes a lead storage battery, a lithium ion battery, a nickel-cadmium (Ni—Cd) battery, and the like, by way of an example.
The lithium ion battery, which is one of the secondary battery, is configured to include an anode generally consisting of carbon, a cathode generally consisting of lithium compounds, an electrolyte disposed between the anode and the cathode, and a wire connecting the anode and the cathode. Lithium ions in the electrolyte moves toward the anode at the time of charging, and moves toward the cathode at the time of discharging, and generate a chemical reaction while discharging surplus electrons from each pole or absorbing surplus electrons thereinto. During this process, electrons flow in the wire, and thus, an electric energy is generated.
Life, energy density, and thermal stability of the lithium secondary battery are mainly determined by the cathode active material. It is known that physical properties of the cathode active material are largely affected by composition of the active material and a method for manufacturing the same.
As a general method for manufacturing the cathode active material, Korean Patent Laid-Open Publication No. 2009-0108964 discloses a solid phase reaction method and Korean Patent Laid-Open Publication No. 2011-0039657 discloses a coprecipitation method. The solid phase reaction method is a method for manufacturing a cathode active material by using carbonate or hydroxide of each element constituting the cathode active material and repeating mixing and heat-treating processes several times, and the coprecipitation method is a method for manufacturing a cathode active material by mixing a precursor with a lithium source, and then performing a heat-treatment, wherein the precursor is prepared by mixing each element constituting the cathode active material except for lithium in a solution, followed by coprecipitation.
However, in the solid phase method, there is a risk in that impurities flow in mixing solid phase raw materials, and since the cathode active materials are manufactured by solid phase diffusion, there is a difficulty in manufacturing a phase having uniform composition and in adjusting a size of final particles, and at the time of manufacturing, energy and time are significantly consumed. In the coprecipitation method, precise control in processes is required to obtain uniform precipitation, pollution caused by additives for precipitation is inevitable, a large amount of waste liquid occurs. In addition, as compared to the solid phase method, the active material manufactured by the coprecipitation method has uniform composition; however, there is still compositional non-uniformity.
Therefore, development of a method for manufacturing a cathode active material having significantly excellent compositional uniformity and high capacity, being free of pollution, and being manufactured by mass-production with a simple process, a short-time, and a low cost, in an environment-friendly manner in which by-products such as waste liquid do not occur, has been urgently demanded.